Light emitting materials of high molecular weight are variously investigated since they are soluble in a solvent and capable of forming a light emitting layer in a light emitting device by an application method, differing from those of low molecular weight, and as the examples, there are known copolymers having two kinds of repeating units containing an aromatic ring in the main chain and having a phenyl group as the end group (formula weight 77), which is an aryl group (International publication Nos. 99/54385, 01/49769, U.S. Pat. No. 5,777,070).
However, when the above-mentioned copolymer is used as a light emitting material for a light emitting layer of a polymer LED, properties as a polymer LED such as time of luminance decreasing, light emitting efficiency and the like of the polymer LED are not practically satisfactory yet, and there is a desire for a copolymer showing more excellent properties when used as a light emitting material of a light emitting layer of a polymer LED.